This invention relates to an electronic device having an indirectly-heated cathode which is heated solely by electrons which are emitted from an associated unheated auxiliary field-emission cathode.
It has been suggested previously to heat an indirectly-heated cathode by field emission. See, for example, U.S. Pat. Nos.:
2,509,053 TO C. J. Calbick,
2,552,047 TO J. Kurshan,
2,953,701 TO A. J. Gale,
3,474,282 TO H. Katz et al., and
3,521,113 TO A. N. Broers.
Each of these references discloses a main thermionic cathode that is indirectly heated by electrons emitted from an auxiliary cathode, which is itself heated by some other means. The auxiliary cathode may be a thermionic emitter or a field emitter.